We report differential and momentum-transfer cross sections for elastic scattering of electrons by ${\mathrm{NH}}_3$ for collision energies from 2.5 to 20 eV. These cross sections were obtained in the fixed-nuclei static-exchange approximation using the Schwinger variational principle. Although fixed-nuclei cross sections for electron–polar-molecule collisions are inherently divergent at small angles, such results can provide useful estimates of the differential cross sections at intermediate and larger angles. The agreement at intermediate and larger scattering angles between the calculated and relative experimental cross sections, which are available at 8.5 and 15 eV, is good. The differential cross sections also show evidence of a weak d-wave enhancement around 8 eV. A significant feature seen in these cross sections, particularly at 15 and 20 eV, is their substantial backward peaking beyond 120°.

• Received 17 October 1988

DOI:https://doi.org/10.1103/PhysRevA.39.2392